FA-3966 / Text processing / Open access

Character bigram extraction omits the last window · case 01

Character bigram extraction omits the last window.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The implementation applies an operation whose text or grammar semantics violate this contract: Return all overlapping two-codepoint substrings, including the final window.

VERIFIED REPAIR

Implement the complete stated contract, including the boundary fixtures: Return all overlapping two-codepoint substrings, including the final window.

Unsuccessful approach: The attempted repair handles the primary example but still violates a separate boundary of the same contract.

Case contract

Return all overlapping two-codepoint substrings, including the final window.

Why this case matters

A local executable model for consumers of structured text; oracle values are authored literals, not outputs copied from the repaired implementation.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return [x[i:i+2] for i in range(len(x)-2)]
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('abcd'), ['ab', 'bc', 'cd'])
check('boundary 2', solve('ab'), ['ab'])
check('boundary 3', solve('a'), [])
check('boundary 4', solve(''), [])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
boundary 1	`['ab', 'bc']`	`['ab', 'bc', 'cd']`	Failed
boundary 2	`[]`	`['ab']`	Failed
boundary 3	`[]`	`[]`	Passed
boundary 4	`[]`	`[]`	Passed

SHA-256 / 3e02645c606dcc9cce39c0d7c4cca9e2b1496337f153166402ae3caf2339d1bd

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return [x[i:i+2] for i in range(0,len(x)-1,2)]
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('abcd'), ['ab', 'bc', 'cd'])
check('boundary 2', solve('ab'), ['ab'])
check('boundary 3', solve('a'), [])
check('boundary 4', solve(''), [])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
boundary 1	`['ab', 'cd']`	`['ab', 'bc', 'cd']`	Failed
boundary 2	`['ab']`	`['ab']`	Passed
boundary 3	`[]`	`[]`	Passed
boundary 4	`[]`	`[]`	Passed

SHA-256 / cc91edc3b19f8c5f124f7bccb8633bc0adee4a8806458787584b24a8d0fa5cc5

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return [x[i:i+2] for i in range(len(x)-1)]
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('abcd'), ['ab', 'bc', 'cd'])
check('boundary 2', solve('ab'), ['ab'])
check('boundary 3', solve('a'), [])
check('boundary 4', solve(''), [])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
boundary 1	`['ab', 'bc', 'cd']`	`['ab', 'bc', 'cd']`	Passed
boundary 2	`['ab']`	`['ab']`	Passed
boundary 3	`[]`	`[]`	Passed
boundary 4	`[]`	`[]`	Passed

SHA-256 / eacf9ecac8c94eb9a338d52c1e4fc275bbe46bc77ec13b0b3d31c5e628fb0f69

Verification & scope

This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:37:33.572393+00:00.

Case digest / a841c69de5d6ff35147def0efc1337faaa2eee9d90ff4ed955fe0960db760780